1. Field of the Invention
Injectivity profile and vertical conformance of subterranean reservoirs are improved by injecting through an injection means in fluid communication with the reservoir an aqueous solution containing a copolymer obtained by radiation polymerization. Reservoirs especially useful with this invention are those defined as heterogeneous reservoirs or highly stratified reservoirs or reservoirs containing zones having substantially different permeabilities.
2. Description of the Prior Art
It is known that heterogeneous formation zones can "thieve" fluids during secondary or tertiary recovery processes. Such thieving zones generally effect premature fingering during the flooding process. Also, zones of lesser permeabilities are generally by-passed by displacing fluids, thus making a secondary or tertiary flooding process less efficient to displace the oil therefrom.
The prior art has tried to overcome this adversity by plugging the thieving zone. For example, cement, plastics, coal tar products and by-products, cotton seed hulls, etc. have been pumped into the thieving zones. The following patents are representative of the prior art:
U.S. Pat. No. 3,334,689 to McLauthlin stabilizes soil and substrata by consolidating loose sands, grouting, and bridging and plugging openings to render them less permeable to the passage of fluids. Such is accomplished by injecting an aqueous solution of a polymerizable composition containing a monoethylenically unsaturated acrylate monomer and a cross-linking agent.
Fulford, in U.S. Pat. No. 3,621,914, plugs fractures or highly permeable streaks in reservoirs containing kaolinite by introducing an aqueous solution containing hydrazine. The hydrazine attacks the kaolinite and decomposes the clay mineral bonds of the rock matrix.
Scott, Jr. et al, in U.S. Pat. No. 2,734,861, bridge permeable zones in a subterranean strata by injecting a polycyclic aromatic hydrocarbon having a freezing point above 100.degree.F.
Parks, in U.S. Pat. No. 3,583,169, reduces the permeability of porous strata by reacting a basic solution having dispersed therein an organic compound (e.g., lignin or tannin acid) which will form a precipitate when contacted with an acidic solution containing multivalent metallic cations. The reaction product is formed in situ and reduces the permeability of the porous rock.
Eilers, in U.S. Pat. No. 3,421,584, and Pence, Jr., in U.S. Pat. No. 3,502,149, teach the use of polymers in subterranean strata.